The present invention relates to a method of imparting antimicrobial activity to an ophthalmic composition. More particularly, it relates to the use of a particular polymeric quaternary ammonium compound to improve disinfectant and preservative qualities in compositions which come into contact with the eye or with ophthalmic devices, such as contact lenses.
The sensitive nature of the ocular environment mandates antimicrobial methods which provide high bactericidal efficacy coupled with low cytotoxicity. A number of preserving and disinfecting methods are known in the contact lens art. Typically, these methods employ either sorbic acid, thimerosal, chlorhexidine or a conventional quaternary germicide such as benzalkonium chloride. However, these antimicrobial compounds have drawbacks that tend to restrict their use. For example, sorbic acid characteristically contains formaldehyde residues; and thimerosal, chlorhexidine and BAK may cause eye irritation.
U.S. Pat. Nos. 4,525,346 and 4,407,791 to Stark relates to antimicrobial ophthalmic compositions containing the quaternary ammonium compound "1-tris(2-hydroxyethyl)ammonium-2-butenyl-4-poly[1-dimethyl ammonium-2-butenyl]-w-tris(2-hydroxyethyl) ammonium." This compound, however, is unstable in the presence of hydrogen peroxide, which is used in a number of contact lens disinfecting and preserving methods. It is also subject to improvement in bactericidal efficacy, particularly in instances involving Serratia marcescens.
Therefore, there exists a need for an improved method of imparting antimicrobial activity to ophthalmic compositions.
There exists a further need for such a method which utilizes a compound which has low cytotoxicity and high bactericidal efficacy.
There exists a further need for such a method which can be employed regardless of the presence of hydrogen peroxide.